The present invention relates to an outer tubular envelope for covering an elongated inserting portion of an inserting apparatus such as, for example, an endoscope or the like.
In recent years, an industrial endoscope has widely been utilized to inspect an interior of a piping or a machine, in view of such advantage that the interior of the piping or machine can be viewed without disassembling the same.
A general endoscope comprises an operating body, an ocular portion provided at the operating body, and an elongated flexible inserting portion extending from the operating body. The inserting portion is inserted into an interior of an object to be inspected, and the interior of the object is viewed by the ocular portion through an optical viewing system incorporated in the inserting portion.
The conventional inserting portion has an outer peripheral surface thereof covered with an outer tubular envelope formed of a rubber material. However, such outer envelope formed of a rubber material is high in frictional resistance, and this often makes it difficult to insert the inserting portion into the object to be inspected.
In view of the above, it has been proposed that a plurality of strands formed of a slippery material such as, for example, extremely fine steel wires are braided into the form of a tube to form an outer tubular envelope, and the inserting portion is covered with such envelope The outer envelope has an outer peripheral surface thereof which is graduated by paints or inks at constant intervals, to allow an operator to determine a length of the inserting portion inserted into an object to be inspected, in use.
However, the graduations of paints or inks are disadvantageous in that the graduations are rubbed off and disappear, in the course of rubbing against the object to be inspected, during the use for a long period of time.